A panoramic photograph is a photograph with an unusually large field of view, an exaggerated aspect ratio, or both. For example, a horizontal panoramic photograph is much wider than its height, and has a horizontal angle of view that is large in relation to its vertical angle of view. A vertical panoramic photograph is much taller than its width, and has a vertical angle of view that is large in relation to its horizontal angle of view. A panoramic photograph, sometimes called simply a “panorama”, can provide a unique and sometimes striking view of a scene.
Historically, panoramic photographs have been taken using specially-made cameras. One kind of panoramic camera uses a rotating lens and body to sweep across a large field of view while moving film past a narrow exposure slit behind the lens. This kind of rotating camera, sometimes called a “Cirkut-type” camera after an early commercial model, can take a photograph with a field of view of 360 degrees or more. A swing-lens camera operates on a similar principle, but rotates its lens and the exposure slit in relation to a stationary body and film. A swing-lens camera can take a photograph with a field of view somewhat less than 180 degrees.
Another method of making a panoramic photograph is to take several overlapping conventional photographs, each typically having an aspect ratio of about 3:2, and then join them together into a single larger photograph. The joining is typically done using a computer operating on digital representations of the component photographs, for example photographs taken with a digital camera. The process of combining digital images into a larger photograph is often called “stitching” or “mosaicing”. In principle, any number of component images can be stitched, and the resulting panorama can cover a field of view of up to 360 degrees or more.
FIGS. 1A-1D illustrate the process of creating a panoramic photograph from component photographs. FIG. 1A shows a landscape scene 100 with a wide aspect ratio. FIG. 1B shows three overlapping component photographs 101, 102, 103 of a conventional aspect ratio, taken so that each portion of scene 100 that is to be included in the resulting panoramic photograph is represented in at least one of the component photographs 101-103. FIG. 1C shows component photographs 101-103 in isolation. Certain features such as tree 104 and fence corner 105 appear in more than one of the component photographs, and may be used by the stitching process to align component photographs 101-103 with each other. FIG. 1D shows a panoramic photograph 106 constructed by stitching component photographs 101-103 together.
Methods are known in the art for accomplishing the stitching, and are typically computationally-intensive. For example, software performing image stitching may correct distortions, such as lens distortion and perspective distortion, present in the component images before stitching them together. Additionally, finding the proper alignment between component images may involve multiple computations of correlation coefficients that reflect the “goodness” of the alignment between image segments. Variations in tone, caused by effects such as changes in viewing angle and lens vignetting, may be corrected or otherwise accommodated. The time required to perform the stitching increases dramatically with increased size or resolution of the component images.
Some modern digital cameras provide a mode that assists a user of the camera in taking a set of component photographs for later stitching into a panoramic photograph. For example, a panoramic mode may use a display screen on the camera to assist the user in framing each component photograph for proper overlap with a previous photograph in the set, and may ensure consistent exposure settings for all of the component photographs in a set.
At least one digital camera model can perform stitching on a set of low-resolution “screen nail” images so that the photographer can detect obvious problems such as insufficient overlap in the component images. (A “screen nail” is a small low-resolution copy of a digital image, analogous to a “thumbnail” image, and is sized to fit an on-camera display. A typical screen nail image may be, for example, approximately 320 by 240 pixels.) This capability is described in U.S. patent application Ser. No. 11/055,885, filed on Feb. 11, 2005 and having a common assignee with the present application. However, previous digital cameras have not performed the stitching of high- or full-resolution images because the relatively simple processors used in digital cameras could not perform the computationally-intensive stitching algorithms quickly enough to provide a satisfactory user experience. Previously, a camera user who wished to stitch high-resolution component images into a panorama had to upload the component images to a computer and use software executing on the computer to perform the stitching. This prior method required the use of a computer, possibly including installing additional software on the computer, and prevented the user from immediately printing or sharing the panorama.